Low iron, high redox ratio, and high iron, high redox ratio, soda-lime-silica glasses and methods of making same

ABSTRACT

A glass has a basic soda-lime-silica glass portion, and a colorant portion including total iron as Fe 2 O 3  selected from the group of total iron as Fe 2 O 3  in the range of greater than zero to 0.02 weight percent; total iron as Fe 2 O 3  in the range of greater than 0.02 weight percent to less than 0.10 weight percent and total iron as Fe 2 O 3  in the range of 0.10 to 2.00 weight percent; redox ratio in the range of 0.2 to 0.8, and tin and/or tin compounds, e.g. SnO 2  greater than 0.000 to 5.0 weight percent. In one embodiment of the invention, the glass has a tin side and an opposite air side, wherein the tin side of the glass is supported on a molten tin bath during forming of the glass. The tin concentration at the tin side of the glass is greater than, less than, or equal to the tin concentration in “body portion” of the glass. The “body portion” of the glass extending from the air side of the glass toward the tin side and terminating short of the tin side of the glass.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/252,206, filed Apr. 14, 2014, now United States ApplicationPublication No. US2014/0309099A1, published on Oct. 16, 2014, whichapplication claims the benefits of U.S. Provisional Patent ApplicationSer. No. 61/812,006 filed Apr. 15, 2013, and titled “LOW IRON, HIGHREDOX RATIO SODA-LIME-SILICA GLASS AND METHOD OF MAKING SAME”. Thisapplication is also related to application Ser. No. 15/046,938, filedFeb. 18, 2016, which is a divisional of application Ser. No. 14/252,206.Application Ser. Nos. 14/252206, 15/046,938 and 61/812,006 in theirentirety are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to iron containing, high redox ratiosoda-lime-silica glasses and methods of making same, and moreparticularly, to low iron, high redox ratio, and high iron, high redoxratio, soda-lime-silica glasses, and methods of making same.

2. Discussion of Available Technology

As is appreciated by those skilled in the art of making soda-lime-silicaglass, parameters of interest include, but are not limited to the redoxratio, and total iron expressed as Fe₂O₃. For example and not limitingto the discussion, U.S. Pat. No. 6,962,887, which patent is incorporatedherein by reference, discloses a glass having total iron expressed asFe₂O₃ in the range of greater than 0 to 0.02 weight percent (“wt. %”)and a redox ratio in the range of 0.2 to 0.6. The glass is aestheticallypleasing and useful, for example, in furniture applications such astabletops or shelving. Further, this glass is highly transparent whenviewed normal to a major surface of the glass but has an aestheticallydesirable blue i.e., azure edge color when viewed on edge. Such a glassis sold by PPG Industries, Inc. under the PPG Industries Ohio registeredtrademark “Starphire”.

Another glass of interest in the present discussion is disclosed in U.S.Pat. No. 6,313,053, which patent is incorporated herein by reference.The patent discloses a blue colored glass using a standardsoda-lime-silica glass base composition and additionally iron andcobalt, and optionally chromium, as solar radiation absorbing materialsand colorants. The blue colored glass has total iron expressed as Fe₂O₃in the range of 0.10 to 1.0 wt. %, and a redox ratio in the range ofgreater than 0.35 to 0.60. Such a glass is considered for purposes ofdiscussion a high iron, high redox ratio, soda-lime-silica glass. Such aglass is said by PPG Industries, Inc. under the PPG Industries Ohioregistered trademark “Solextra”.

The low iron, and high iron, high redox soda-lime-silica glasscompositions can be made in a multi-stage melting and vacuum-assistedrefining operation as disclosed in U.S. Pat. Nos. 4,792,536 and5,030,584, and can be made in a conventional float glass system asdisclosed in U.S. Pat. No. 6,962,887. U.S. Pat. Nos. 4,792,536,5,030,594 and 6,962,887 are hereby incorporated by reference. The highiron, and low iron, high redox ratio soda-lime-silica glass compositionsare generally made in a conventional float glass system using oxyfuel asdisclosed in U.S. Pat. Nos. 4,604,123; 6,962,887 and 7,691,763 to obtainor maintain a high redox ratio, and the low iron, high redox glasses canbe made using oxyfuel fired furnaces but are preferably made using fueland air mixtures fired in Siemens type furnaces. U.S. Pat. Nos.4,604,123; 6,962,887 and 7,691,763 are hereby incorporated by reference.Although the presently available methods for making the glassesdisclosed in U.S. Pat. Nos. 4,792,536, 5,030,594, 6,313,053 and6,962,887 are acceptable; there are limitations. More particularly, thelimitations of interest in the present discussion are maintaining theredox ratio of the glasses within a range of 0.2 to 0.6 and preferablywithin the range of 0.35 to 0.6.

As is appreciated by those skilled in the art, the redox ratio can beincreased by additions of sulfur (see incorporated U.S. patents) andcarbon, e.g. but not limited to graphite, coal and/or oil to reduce theFerric iron (Fe+++) to Ferrous iron (Fe++). Although presently there areavailable methods for making glasses having low iron, high redox ratio,and high iron, high redox ratios, it is appreciated by those skilled inthe art that the methods are usually tailored to meet the parameters ofthe furnace. More particularly, the use of carbon to increase the redoxratio of soda-lime-silica glasses made using oxyfuel fired glassmakingfurnaces can result in batch melting changes that can result in silicastones. In view of the forgoing, it would be advantageous to providemethods for making low iron and high iron soda-lime-silica glasseshaving high redox ratios that can be used regardless of the type ofheating system or furnace used to melt the glass batch materials and toeliminate the limitations associated with the heating systems.

SUMMARY OF THE INVENTION

This invention relates to, but is not limited to, a method of making aglass, including but not limited to providing a basic soda-lime-silicaglass portion, and a colorant portion, the colorant portion, including,but not limited to total iron as Fe₂O₃ in the range of greater than zeroto 2.00 weight percent, a redox ratio in the range of 0.20 to 0.60 andtin and/or tin containing compounds providing tin in an amount withinthe range of greater than 0.005 to 5.0 weight percent. The glass portionand the colorant portion are melted to provide a pool of molten glassthat is flowed onto a molten tin bath. The molten glass moves on thesurface of the molten tin bath, while the glass is controllably cooledand forces are applied to the glass to provide a glass of a desiredthickness. Thereafter the glass is removed from the molten tin bath,wherein the tin and/or tin containing compounds concentration at the tinside of the glass are greater than the tin concentration in body portionof the glass, the body portion of the glass extending from the air sideof the glass and terminating short of the tin side of the glass.

In one non-limiting embodiment of the invention the total iron as Fe₂O₃in the range of greater than zero to 0.02 weight percent.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are a horizontal section of a glass melting furnace thatcan be used in the practice of the invention; FIG. 1A is the meltingsection of the furnace, and FIG. 1B is the refining and homogenizingsection of the furnace.

FIG. 2 is a vertical section of the melting section shown in FIG. 1A.

FIG. 3 is an elevated side view partially in cross section of a glassmelting and refining apparatus that can be used in the practice of theinvention.

FIG. 4 shows a set of measurements of low iron, soda-lime-silica glasslaboratory samples to show the effect of graphite and tin dioxide on theredox ratio. A straight line connects the measurements for each samplehaving similar amounts of graphite. The batch for each sample was meltedat a temperature of 2650° F.

FIG. 5 shows a set of measurements of low iron, soda-lime-silica glasslaboratory samples (1) to show the effect of temperature, (2) to showthe effect of tin dioxide added to the batch, and (3) to compare tindioxide added to the batch to glass with tin dioxide already in theglass as 100% cullet. The samples were free of graphite and a straightline connects samples from batches heated at the respective melttemperature.

FIG. 6 shows a set of measurements of low iron, soda-lime-silica glasslaboratory samples showing the effect tin compounds on the redox ratio.The batch was melted at 2650° F. and a straight line connects commonmeasurements.

FIG. 7 shows a comparative set of measurements between low iron glassesproduced during a plant trial in a real furnace under real operatingconditions to low iron glasses from laboratory melts.

FIG. 8 shows a set of measurements of high iron soda-lime-silicate glasssamples showing the effect of graphite, temperature, tin dioxide and tinon the redox ratio. A straight line connects common measurements.

FIG. 9 is a fragmented side view of a glass ribbon supported on a moltentin bath.

DETAILED DESCRIPTION OF THE INVENTION

As used in the following discussion, spatial or directional terms, suchas “top”, “bottom”, and the like, relate to the invention as it is shownin the drawing figures. However, it is to be understood that theinvention can assume various alternative orientations and, accordingly,such terms are not to be considered as limiting. Unless otherwiseindicated, all numbers expressing dimensions, physical characteristics,quantities of ingredients, reaction conditions, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical values set forth in the following specificationand claims can vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques. Moreover, all ranges disclosedherein are to be understood to include the beginning and ending rangevalues and to encompass any and all subranges subsumed therein. Forexample, a stated range of “1 to 10” should be considered to include anyand all subranges between (and inclusive of) the minimum value of 1 andthe maximum value of 10; that is, all subranges beginning with a minimumvalue of 1 or more and ending with a maximum value of 10 or less, e.g.,5.5 to 10. Additionally, all documents, such as but not limited toissued patents and patent applications, referred to herein are to beconsidered to be “incorporated by reference” in their entirety. Further,as used herein, the term “over”, means formed, applied, deposited, orprovided on but not necessarily in contact with the surface. Forexample, a coating layer formed or applied “over” a substrate surfacedoes not preclude the presence of one or more other coating layers orfilms of the same or different composition located between the formedcoating layer and the surface of the substrate. Still further the term“on” means formed, applied, deposited, or provided on and in contactwith the surface.

In one non-limiting embodiment of the invention, the invention ispracticed making soda-lime-silica glasses having a low iron content,e.g. but not limited to total iron Fe₂O₃ in the range of greater than0.00-0.02 wt. % and a redox ratio in the range of 0.2-0.6, e.g. but notlimited to a glass disclosed in U.S. Pat. No. 6,962,887.

In another non-limiting embodiment of the invention, the invention ispracticed to make soda-lime-silica glasses having a high iron Fe₂O₃content, e,g. but not limited to Fe₂O₃ in the range of equal to andgreater than 0.1 wt. % and a redox ratio in the range of 0.2-0.6, e.g.but not limited to a glass disclosed in U.S. Pat. No. 6,313,053. In thepractice of the invention, any known glass making process can be use tomake the high iron, high redox ratio glass, and the low iron, high redoxratio glass, of the invention.

Any reference to composition amounts, unless otherwise specified, is “byweight percent” based on the total weight of the final glasscomposition. The “total iron” content of the glass compositionsdisclosed herein is expressed in terms of Fe₂O₃ in accordance withstandard analytical practice, regardless of the form actually present.Likewise, the amount of iron in the ferrous state is reported as FeO,even though it may not actually be present in the glass as FeO. Theterms “redox”, “redox ratio” or “iron redox ratio” mean the amount ofiron in the ferrous state (expressed as FeO) divided by the amount oftotal iron (expressed as Fe₂O₃). As used herein soda-lime-silica glasseshaving total iron (expressed as Fe₂O₃) in the range of greater than 0 to0.02 wt. % is a low iron soda-lime-silica glass; glasses having totaliron in the range of equal to and greater than 0.02 to 0.10 wt. % is amedium iron soda-lime-silica glass, and soda-lime-silica glasses havingtotal iron equal to and greater than 0.10 wt. % is a high iron glass.Generally and not limiting to the invention, high iron soda-lime-silicaglasses have total iron in the range of equal to and greater than 0.10wt. % to 2.0 wt. %; equal to and greater than 0.10 wt. % to 1.5 wt. %;equal to and greater than 0.10 wt. % to 1.0 wt. %; and equal to andgreater than 0.10 wt. % to 0.80 wt. %.

The high redox ratio is in the range of equal to 0.2 to 0.6, theinvention, however, is not limited thereto and contemplates ranges of0.3 to 0.6, 0.4 to 0.6 and 0.5 to 0.6. The glass disclosed in U.S. Pat.No. 6,962,887 has a redox ratio in the range of 0.2-0.6 and a total iron(expressed as Fe₂O₃) in the range of greater than 0 to equal to 0.02 wt.% and is a low iron soda-lime-silica glass. The glass disclosed in U.S.Pat. No. 6,313,053 has a redox ratio in the range of 0.2-0.6 and a totaliron (expressed as Fe₂O₃) in the range equal to 0.10 wt. % to 0.90 wt. %and is a high iron soda-lime-silica glass.

As can now be appreciated, the invention is directed to making highiron, high redox soda-lime-silica glasses and low iron, high redoxsoda-lime-silica glasses and is not limited to the optical properties,e.g. ultra violet, visible and IR transmission and absorption and thecolor of the glass and physical properties, e.g. glass thickness. Indefining a non-limiting embodiment of a glass of the invention referencecan be made to specific ranges or values of ultra violet, visible and IRtransmission and absorption, and/or color of the glass and/or physicalproperties, e.g. glass thickness to identify a specific glass of theinvention and/or a glass made by the practice of the invention.Presented below are common additives, e.g. color additives that areadded to the glass batch materials, and/or molten glass to alter opticaland physical properties of the glasses of the invention.

The “sulfur” content of the glass compositions disclosed herein isexpressed in terms of SO₃ in accordance with standard analyticalpractice, regardless of the form actually present.

As used herein, “visible transmittance” and “dominant wavelength” valuesare those determined using the conventional CIE Illuminant C and2-degree observer angle. Those skilled in the art will understand thatproperties such as visible transmittance and dominant wavelength can becalculated at an equivalent standard thickness, e.g., 5.5 millimeters(“mm”), even though the actual thickness of a measured glass sample isdifferent than the standard thickness.

A non-limiting embodiment of the present invention is practiced to makea low iron, high redox glass, e.g. but not limited to the type disclosedin U.S. Pat. No. 6,962,887, that provides an aesthetically desirableglass that is high in visible light transmittance in a normal (i.e.perpendicular) direction to a sheet of the glass but has anaesthetically pleasing blue or azure edge color when viewed on edge. By“high visible light transmittance” is meant visible light transmittancegreater than or equal to 85%, such as greater than or equal to 87%, suchas greater than or equal to 90%, such as greater than or equal to 91%,such as greater than or equal to 92%, at 5.5 mm equivalent thickness forglass from 2 mm to 25 mm sheet thickness. By “visible light” is meantelectromagnetic radiation having a wavelength in the range of 380nanometers (nm) to 770 nm. By “blue edge color” or “azure edge color”glass is meant having a dominant wavelength in the range of 480nanometers (“nm”) to 510 nm, such as in the range of 485 nm to 505 nm,such as in the range of 486 nm to 500 nm, such as in the range of 487 nmto 497 nm, when viewed on edge at an equivalent thickness of 5.5 mm.

In another non-limiting embodiment of the present invention, the presentinvention is practiced to make a high iron Fe₂O₃, high redox glass, e.g.but not limited to the type disclosed in U.S. Pat. No. 6,313,053 thatprovides a blue colored glass using a standard soda-lime-silica glassbase composition and additionally iron and cobalt, and optionallychromium, as solar radiation absorbing materials and colorants. Inparticular, the blue colored glass includes about 0.40 to 1.0 wt. %total iron Fe₂O₃, preferably about 0.50 to 0.75 wt. %, about 4 to 40 PPMCoO, preferably about 4 to 20 PPM, and 0 to 100 PPM chromium oxide(“Cr₂O₃”). The redox ratio for the glass of the present invention isgreater than 0.35 to 0.60, and preferably between 0.35 to 0.50. In oneparticular embodiment of the invention, the glass has a luminoustransmittance of at least 55% and a color characterized by a dominantwavelength of 485 to 489 nanometers and an excitation purity of about 3to 18 percent. In another embodiment of the invention, the glass has aluminous transmittance of at least 65% at a thickness of about 0.154inches (3.9 mm) and a color characterized by a dominant wavelength of485 to 492 nanometers and an excitation purity of about 3 to 18 percent.

As is appreciated, the invention is not limited to the color additivesdiscussed above and any color additives to a soda-lime-silica glassknown in the art can be used in the practice of the invention, forexample, but not limited to the colorants selected from the group ofCoO, Se, NiO, Cl, V2O5, CeO₂, Cr₂O₃, TiO2, Er₂O₃, Nd₂O₃, MnO₂, La₂O₃ andcombinations thereof.

As can now be appreciated, the invention is not limited to the processof, and/or equipment for, practicing the invention to make glasses ofthe invention, and any of the glass making processes and/or equipmentknown in the art can be used in the practice of the invention.

Referring to FIGS. 1 and 2 as needed, there is shown a conventionalcontinuously fed, cross-tank fired, glass melting and non-vacuumrefining furnace 20 having an enclosure formed by a bottom 22, roof 24,and sidewalls 26 made of refractory materials. The glass batch materials28 are introduced through inlet opening 30 in an extension 32 of thefurnace 20 known as the fill doghouse in any convenient or usual mannerto form a blanket 34 floating on surface 36 of molten glass 38. Overallprogression of the glass as shown in FIGS. 1A and 1B is from left toright in the figures, toward entrance end of a glass forming chamber 40of the type used in the art to make float flat glass.

Flames (not shown) to melt the batch materials 28 and to heat the moltenglass 38 issue from burner ports 42 spaced along the sidewalls 26 (seeFIG. 2) and are directed onto and across the surface 36 of the moltenglass 38. As is known by those skilled in the art, during the first halfof a heating cycle, the flames issue from a nozzle 43 (see FIG. 2) ineach of the ports on one side of the tank 20, as the exhaust of thefurnace moves through the ports on the opposite side of the furnace.During the second half of the heating cycle, the function of the portsis reversed, and the exhaust ports are the firing ports, and the firingports are the exhaust ports. The firing cycle for furnaces of the typeshown in FIGS. 1 and 2 are well known in the art and no furtherdiscussion is deemed necessary. As can be appreciated by those skilledin the art, the invention contemplates using a mixture of air and fuelgas, or a mixture of oxygen and fuel gas, to generate the flames to heatthe batch materials and the molten glass. For a discussion of usingoxygen and fuel gas in the furnace of the type shown in FIG. 1,reference can be made to U.S. Pat. Nos. 4,604,123; 6,962,887; 7,691,763,and 8,420,928, which patents are hereby incorporated by reference.

The glass batch materials 28 as they move downstream from the batchfeeding end or doghouse end wall 46 are melted in the melting section 48of the furnace 20, and the molten glass 38 moves through waist 54 torefining section 56 of the furnace 20. In the refining section 56,bubbles in the molten glass 38 are removed, and the molten glass 38 ismixed or homogenized as the molten glass passes through the refiningsection 56. The molten glass 38 is delivered in any convenient or usualmanner from the refining section 56 onto a pool of molten metal (notshown) contained in the glass-forming chamber 40. As the deliveredmolten glass 38 moves through the glass-forming chamber 40 on the poolof molten metal (not shown), the molten glass is sized and cooled. Adimensionally stable sized glass ribbon (not shown) moves out of theglass-forming chamber 40 into an annealing lehr (not shown). Glassmaking apparatus of the type shown in FIGS. 1 and 2, and of the typediscussed above are well known in the art and no further discussion isdeemed necessary.

Shown in FIG. 3 is continuously fed glass melting and vacuum refiningequipment 78 for melting glass batch materials and refining the moltenglass. Batch materials 80, preferably in a pulverulent state, are fedinto cavity 82 of a liquefying vessel, e.g. a rotating drum 84. A layer86 of the batch material 80 is retained on the interior walls of thevessel 84 aided by the rotation of the drum and serves as an insulatinglining. As the batch material 80 on the surface of the lining 84 isexposed to the heat within the cavity 82, it forms a liquefied layer 88that flows out of a central drain opening 90 at the bottom 92 of thevessel 84 to a dissolving vessel 94 to complete the dissolution ofunmelted particles in the liquefied material coming from the vessel 84.

A valve 96 controls the flow of material from the dissolving vessel 94into a generally cylindrical vertically upright vessel 98 having aninterior ceramic refractory lining (not shown) shrouded in a gas-tight,water-cooled casing 100. A molten stream 102 of refined glass fallsfreely from the bottom of the refining vessel 98 and can be passed to asubsequent stage in the glass making process. For a detailed discussionon the operation of the equipment 78 shown in FIG. 3 reference can bemade to U.S. Pat. No. 4,792,536.

The glasses of the invention can be made using any known glass makingprocess. For example, but not limiting to the invention, the low iron,and high iron, high redox glasses of the invention can be made in themulti-stage melting and vacuum-assisted refining operation shown in FIG.3. The refining stage of this known process is performed under a vacuumto reduce the concentration of dissolved gasses and volatile gaseouscomponents, particularly sulfur-containing components. As will beappreciated by one skilled in the art, it can be advantageous to removesulfur-containing components from certain float glass compositions sincethe combination of sulfur with iron in the glass can result in ambercoloration of the glass at high redox ratios, for example, iron redoxratios above 0.4, especially above 0.5, due to the formation of ferricsulfide (also conventionally referred to as iron sulfide or ironpolysulfide). Ferric sulfide can form throughout the bulk glass or instreaks or layers of a glass sheet. As used herein, the term “bulkglass” means the internal portion of a glass piece, such as a glasssheet, that is not chemically altered in the process of forming theglass. For a 2 millimeter (“mm”) or thicker glass sheet made by a floatglass process, the bulk glass does not include the outer region of theglass adjacent the glass surface, for example the outer 26 microns (asmeasured from the glass surface). The elimination of gaseous sulfurcomponents in the vacuum refining stage of this known process helpsprevent the formation of ferric sulfide in the glass and, thus, helpsprevent amber coloration.

In the preferred practice of the invention, the glass of the inventionis made using a conventional non-vacuum float glass system. By“conventional” or “non-vacuum” float glass system is meant that themolten glass is not subjected to a vacuum stage such as that in U.S.Pat. Nos. 4,792,536 and 5,030,594 during the glass melting or refiningoperations. In one embodiment of the invention, the glass can beessentially free of sulfur. By “essentially free of sulfur” is meantthat no intentional addition of sulfur-containing compounds is made tothe glass composition. However, trace amounts of sulfur can be presentin the glass due to impurities in the batch materials or other sources,including cullet. By “trace amounts of sulfur” is meant sulfur in therange of greater than 0% to 0.03 wt. %. In another embodiment,sulfur-containing materials, such as sulfur-containing refining aids,can be intentionally added to the glass composition, e.g., to improvethe melting characteristics of the glass batch materials. However, inthis embodiment, if such sulfur-containing materials are intentionallyadded, they can be added such that the retained sulfur content (e.g.,the average amount of SO₃ left in the resultant bulk glass) is less thanor equal to 0.2 wt. %, such as less than or equal to 0.16 wt. %, such asless than 0.11 wt. %, such as less than or equal to 0.1 wt. %, such asless than or equal to 0.08 wt. %, such as less than or equal to 0.05 wt.%. In one embodiment, the residual sulfur can be in the range of 0.005wt. % to 0.2 wt. %.

As mentioned above and as shown in FIGS. 1 and 2 conventional floatglass systems typically include a furnace or melter into which the glassbatch materials are placed for melting. In one practice of theinvention, the melter can be an oxygen fuel furnace in which the fuel ismixed with oxygen to supply heat to melt the batch materials. In anotherpractice of the invention, the melter can be a conventional air-fuelmelter in which air is mixed with the combustion fuel to provide heat tomelt the batch materials. In a still further practice of the invention,the melter can be a hybrid-type melter in which a conventional air-typemelter is augmented with oxygen latices to supplement the heated airwith oxygen before combustion.

One difference between glasses made from batch materials melted in anoxygen fuel furnace and a conventional air-fuel melter is that the glassmade from batch materials melted in an oxygen fuel furnace typically hasa water content in the range of 425-600 parts per million, whereas theglass made from batch materials melted in a conventional air-fuel meltertypically has a water content in the range of 200-400 parts per million,and glass made from 100% cullet melted in an oxygen fuel furnacetypically has a water content of about 700 parts per million. In thepreferred practice of the invention, the glass batch materials aremelted in an oxygen fuel furnace or a conventional air-fuel melter. Inthe following discussion of the invention, the invention is practicedusing an oxygen fuel furnace, however, the invention is not limitedthereto, and the invention can be practiced using any type of glassmelting system.

In one non-limited embodiment of the invention, the redox ratio iswithin the range of 0.2 to 0.6, and the total iron (Fe₂O₃) is within therange of greater than 0 to 0.02 wt. %, and in another non-limitedembodiment of the invention, the redox ratio is within the range of 0.2to 0.6, and the total iron (Fe₂O₃) is within the range of 0.10 to 2.0wt. %. In the practice of the invention typical batch materials formaking soda-lime-silica glass are introduced into the melter, thefurnace 20 shown in FIG. 1 and furnace 84 shown in FIG. 3. Typical batchmaterials for a soda-lime-silica glass composition include sand, sodaash, limestone, alumina and dolomite. As will be appreciated by oneskilled in the art, conventional soda-lime-silica batch materials alsoinclude melting and refining aids, such as salt cake (sodium sulfate).Salt cake can also be an oxidizer when incorporated into the glassbatch. As discussed above, the presence of sulfur with iron can lead toamber or yellowish coloration on the bottom surface of the float glassribbon due to the local formation of iron polysulfides at or near thebottom surface of the glass. Therefore, in one aspect of the invention,to reduce retained sulfate and subsequent coloration from ironpolysulfide, no sulfur-containing melting and refining aid materials,e.g., salt cake, are intentionally added to the glass batch materials.Due to the absence of the salt cake, melting the batch materials can bemore difficult than would be with the salt cake. Therefore, to offsetthe absence of salt cake, the temperature in the melter can be increasedand/or the throughput of the melter can be decreased to providesufficient melting of the batch materials. Typical batch materials tomake a soda-lime-silicate glass can be selected to provide a final glassproduct having a high iron, high redox ratio glass, or a low iron, highredox ratio glass having the ingredients in the weight percent rangesshown in following Table 1:

TABLE 1 Ingredient Range of Ingredient in Weight Percent SiO₂ 65-75 Na₂O10-20 CaO  5-15 MgO 0-5 Al₂O₃ 0-5 K₂O 0-5 Sn0₂ greater than 0 to 5

In the preferred non-limiting embodiment of the invention, the redoxratio is increased by the addition of tin alone, and/or in combinationwith other additives, to the glass batch materials and/or molten glass,and/or temperature increases to melt the glass batch materials and/orheat the molten glass, to reduce the ferric iron (Fe+++) to the ferrousiron (Fe++). As is appreciated the invention contemplates changing glasscampaigns from making soda-lime-silica glasses having low iron redoxratio to soda-lime-silica glasses having high iron redox ratio, andchanging glass campaigns from making soda-lime-silica glasses havinghigh iron redox ratio to soda-lime-silica glasses having low iron redoxratio.

The following discussion is directed to additives to reduce the ferriciron (Fe+++) to the ferrous iron (Fe++) to increase the redox ratioand/or to maintain the redox ratio in the range of 0.2 to 0.6. The glassin this non-limiting embodiment of the invention is a low iron, highredox glass of the type disclosed in, but not limited to U.S. Pat. No.6,962,887. To provide the azure edge color, a colorant portion can beadded to the batch materials. In one embodiment, the colorant portioncan include one or more iron-containing compounds with the total iron(Fe₂O₃) being less than 0.02 wt. %, such as in the range of 0.007 to0.02 wt. %. Additional or alternative colorants can include one or moreof cobalt oxide (CoO) such as in the range of 0 ppm to 5 ppm, neodymiumoxide (Nd₂O₃) in the range of 0 wt. % to 0.1 wt. %, and/or copper oxide(CuO) in the range of 0 wt. % to 0.03 wt. %. The redox ratio of theglass can be controlled in accordance to the invention to be within therange of 0.2 to 0.6, such as 0.3-0.5, such as 0.4 to 0.6, such as0.4-0.5, such as 0.6. In one embodiment of the invention, the glassbatch materials can be essentially free of sulfur, i.e., no intentionaladdition of sulfur-containing materials is made to the batch materials.However, as will be appreciated by one skilled in the art, sulfur couldbe present from other sources, such as impurities in the batch materialsand/or cullet.

If salt cake is totally eliminated from the batch materials, in additionto increased melting difficulties, the redox ratio of the glass canincrease to the point where polysulfides can be formed in the bulkglass, thus providing the bulk glass with an amber tint. In order tocontrol the redox ratio of the glass, non-sulfur containing oxidizerscan be added to the batch materials in place of salt cake to oxidize theFe++ to Fe+++ to decrease the redox ratio. One non-limiting example ofsuch a material is sodium nitrate (NaNO₃). While sodium nitrate canprevent the redox ratio of the glass from increasing to the point wherebulk polysulfide formation results in an undesirable amber tint in thebulk glass, sodium nitrate can lead to the production of NO_(x)emissions during the glass production process. These NO_(x) emissionscan be treated in conventional manner before release of the meltergasses to the atmosphere to meet governmental restrictions on NO_(x)emissions.

In a further embodiment, manganese oxide (MnO₂) and cerium oxide (CeO₂)can be added to the batch materials to control the redox. Manganeseoxide is used in concentration of 0-1.0 wt. % and preferably greaterthan 0 to 1.0 wt. %. Cerium oxide can be very effective even atconcentrations in the range of greater than 0 wt. % to 0.2 wt. %, suchas less than or equal to 0.1 wt. %. One result of the use of ceriumoxide is that it can cause surface fluorescence when the glass isexposed to ultraviolet light, such as that present in normal sunlight.

In a still further embodiment of the invention, rather than completelyeliminating salt cake from the batch materials, a mixture of salt cakeand one or more non-sulfur containing oxidizing materials, such as butnot limited to sodium nitrate, manganese dioxide, and/or cerium oxide,can be added to the batch materials to aid in melting and refining thebatch materials. If salt cake is present, the initial introduction ofnon-sulfur-containing oxidizing materials can result in increasedretention of sulfate but ultimately the amount of salt cake added to thebatch materials can be controlled to provide a final glass product thatis substantially free of sulfur. By “substantially free of sulfur” ismeant that residual sulfur (i.e., SO₃) in the bulk glass is less than orequal to 0.2 wt. %, such as less than or equal to 0.15 wt. %, such asless than or equal to 0.11 wt. %, such as less than or equal to 0.1 wt.%, such as less than or equal to 0.08 wt. %, such as less than or equalto 0.05 wt. %. The utilization of both salt cake and non-sulfurcontaining oxidizing agents can maintain the melting and refiningconditions of the glass batch materials and redox ratio of the glasswithout leading to or promoting the undesirable formation ofpolysulfides at the region adjacent the bottom of the glass.

In a still further embodiment of the invention, the melter can be anoxygen fuel furnace. It has been observed that for batch materialshaving a given level of salt cake, the retained sulfate in the resultantglass when the batch materials are melted using an oxygen fuel furnaceis less than that retained for the same glass batch composition using aconventional air furnace. Thus, salt cake or another sulfur-containingoxidizer can be added to the batch materials and melted in an oxygenfuel furnace to provide lower retained sulfate than would be present ifthe same batch composition were melted in a conventional air-fuelfurnace. In this embodiment, the sulfur-containing batch material shouldbe added at a level to provide a glass product that is substantiallyfree of sulfur.

Thus, as discussed above, the formation of undesirable amber colorationin the glass can be reduced or eliminated by adjusting and/or selectingthe components of the glass composition. However, in another aspect ofthe invention, this undesirable amber coloration can be affected byadditionally or alternatively controlling the amount of dissolved ironin the molten metal of the molten metal bath.

In a float glass process, molten glass flows from a furnace onto a poolof molten tin in a float bath to form a float glass ribbon. During thefloat process, oxygen from the bottom surface of the float glass ribbon,i.e., the surface of the ribbon in contact with the molten tin, candiffuse into the molten tin. Consequently, multivalent ions at thebottom surface of the glass can become chemically reduced. For example,sulfur in or near the bottom surface of the glass can be reduced fromS⁺⁶ (hexavalent sulfur) to S⁻² (sulfide). These sulfides can react withiron, particularly ferric iron (Fe⁺³), to form iron polysulfides at thebottom surface of the glass ribbon. The iron can already be present inthe glass or, in some instances, iron present in the molten tin candiffuse into the bottom surface of the glass to react with the sulfides.Iron polysulfide is a powerful colorant and can produce a region orlayer of amber color several microns thick in the bottom of the glassribbon. Thus, if one were to look through the edge of the resultantglass sheet at an oblique angle, the region of amber coloration on thebottom of the glass can make blue glass appear green or yellowish-green.This perceived color shift of the glass edge at oblique viewing anglesis not aesthetically desirable for most applications. The undesirableeffect of amber coloration on the bottom surface of the glass can alsobe present in other tinted glass, such as those having a bulk glasscolor of green or bluish green.

As will be appreciated by one of ordinary skill in the glass making art,medium iron float glass and low iron float glass is particularlysusceptible to an iridescent bloom formation on the bottom surface.During the float glass forming process, tin oxide (SnO) from the tinbath can diffuse into the bottom surface of the float glass ribbon. Whenthe resultant glass is reheated in the presence of oxygen, e.g., air,such as during bending, tempering, or sagging operations, highlyconcentrated tin oxide (SnO) on the bottom surface of the glass canoxidize to form tin dioxide (SnO₂). The subsequent microscopic volumeexpansion can cause the appearance of an iridescent haze on the glass.U.S. Pat. No. 3,305,337 teaches adding certain reactive elements,including iron, to the tin bath can capture oxygen, thus reducing themigration of tin oxide into the bottom of the glass and, therefore, thepotential for bloom formation. Under equilibrium conditions, a givenconcentration of iron in the molten tin will be reached as a function ofthe concentration of iron in the glass. For example, while producing amedium iron float glass with a concentration of 0.1 wt. % iron oxide,the equilibrium concentration of iron in the molten tin bath can beabout 0.01 wt. % Fe. If the concentration of iron in the tin isincreased to 0.04 wt. % by a deliberate addition of iron to reduce thepotential for bloom formation, increased diffusion of iron from the tinbath into the bottom surface of the glass can raise the averageconcentration of iron in the bottom surface of the glass to about 0.2wt. % iron oxide. This additional iron in the bottom surface of theglass can react with sulfur (particularly sulfides S⁻²) to form ironpolysulfides to produce an amber color center. Therefore, in order todecrease the formation of the iron polysulfide color centers at thebottom surface of the glass, the molten tin is substantially free ofiron. By “substantially free of iron” is meant that no or substantiallyno iron is intentionally added to the molten tin. In one embodiment, theconcentration of iron (Fe) in the molten tin is less than or equal to0.05 wt. %, such as less than or equal to 0.04 wt. %, such as less thanor equal to 0.03 wt. %, such as less than or equal to 0.02 wt. %, suchas less than or equal to 0.01 wt. % based on the total weight of themolten metal. Therefore, in one aspect of the invention, no iron isintentionally added to the molten tin, e.g., for two or more monthsprior to or during production of the low iron glass of the invention.

As will be appreciated by one skilled in the art, even though no ironmay be intentionally added to the molten tin, iron concentrationsgreater than those desired above could still be present in the moltentin as a consequence of the previous production of glass having a higheriron content than the desired ranges disclosed above. Therefore, themolten tin can be treated, e.g., cleaned, to remove dissolved iron asdisclosed in U.S. Pat. No. 8,962,887.

The discussion is now directed to non-limiting embodiments of theinvention to increase the redox ratio by the addition of tin and tincontaining compounds to the glass batch materials and/or to the moltenglass to reduce the ferric iron (Fe+++) to the ferrous iron (Fe++). Inthe preferred practice of the invention, tin and/or tin containingcompounds are added to the glass batch materials and/or molten glass inany convenient manner, e.g. but not limited to (1) adding SnO₂ and/ortin sulfate (“SnS”) to the glass batch materials as a dry powder; (2)adding pellets of SnO₂ to the glass batch materials; (3) adding glasscullet to the batch material, the cullet having a coating of SnO₂ overand/or on a glass surface and/or glass cullet having tin and/or tincontaining compounds within the body of the glass; (4) adding groundparticles of tin and/or tin containing compounds, e.g. but not limitedto Sn, SnO₂, and SnS to the glass batch materials; (6) mixing dry SnO₂with a liquid to make a slurry and adding the slurry to the batchmaterials; (7) bubble tin containing gas, e.g. but not limited theretotin halogens, e.g. but not limited to tin chloride (“SnCl₄”) into themolten glass in the furnace or melter using the bubblers 150 shown inFIGS. 1A and 2, (8) adding organo-tin compounds and organo-tin compoundscontaining halogens, e.g. but not limited to Sn(C₄H₉)₃H.

In the preferred practice of the invention, tin and/or tin dioxide isadded to the glass batch and molten glass in the furnace 20 (FIG. 1A) ormelter 84 (FIG. 3); the invention, however, is not limited thereto andtin oxides, tin oxynitrides, tin nitrides, tin halogens, to name a fewand combinations thereof can be added to provide tin ions to increasethe redox ratio.

It is believed that the reaction to reduce the ferric iron (Fe+++) tothe ferrous iron (Fe++) in the resultant glass is better appreciated bythe following discussion:

Sn⁴⁺=Sn²⁺+2e ⁻  Equation 1

Sn²⁺+2Fe³⁺+2e ⁻=Sn⁴⁺+2Fe²⁺  Equation 2

Equations Discussion:

Equation 1 shows reactions believed to occur where the Sn⁴⁺ ions (SnO₂)that are added at room temperature become reduced to Sn²⁺ ions (SnO)plus two electrons when the material is heated and incorporated into theglass structure. Those 2 electrons from the single Sn⁴⁺ ion canfacilitate reduction of two ferric iron (Fe+++) ions to two ferrous iron(Fe++) ions while the glass is cooling as shown in Equation 2.Essentially the Sn²⁺ ions prefer the Sn⁴⁺ state at some temperaturelower than melting temperatures and thus reduction of the iron ionsoccurs while the ions can still transfer charge. The total tin contentin the final glass products described in the preferred embodiment ofthis invention is reported as weight percent of SnO₂ regardless of theactual concentration of Sn++ versus Sn++++ ions. This helps to assessthe total tin ion content of the product or glass sample withoutdirectly measuring the Sn++ or Sn++++ ion content, which is inherentlyrelated to the added batch components that contain tin ions in eithervalence state or via other means of adding tin as described in thepractice of the invention. The total content of tin ions in glasssamples is reported as SnO₂ in weight percent measured by X-rayFluorescence (XRF) spectroscopy. The total tin ion content described asSnO₂ can be measured via characteristic K alpha x-rays from tin ions,but the preferred method utilizes characteristic L alpha x-rays from tinions for a more robust quantification.

Laboratory melts were made to determine the effect of tin alone or incombination with temperature changes and/or graphite. The batch for thesoda-lime-silica glass included the material listed in TABLE 2 below:

TABLE 2 Material Amount Low iron sand 369.44 grams Soda Ash 119.96 gramsLow iron Limestone 38.83 grams Low iron dolomite 73.36 grams Graphite(when added) 0.303 grams Iron oxide from sand 70 parts per million

The batch materials were heated in 50° F. steps within a temperaturerange 2450° F. to 2600° F. in a platinum crucible. The batch was heatedfor a period of ½ hour at each step and for 1 hour at 2600° F. Themelted batch was fritted (placed in water) and placed in a platinumcrucible and heated to a temperature of 2650° F. or 2800° F. (as notedbelow), and held at that temperature for 2 hours. The melt was poured ona metal sheet and annealed at a temperature near 1130° F. Specimens werecut from the annealed glass and the redox ratio of the specimensdetermined. Preparing laboratory glass samples and determining the redoxratio of soda-lime-glass are well known in the art and no furtherdiscussion is deemed necessary.

It has been concluded from the results of the laboratory melts thattemperature and/or carbon based reducing agents, e.g. but not limited tographite, in combination with tin dioxide (SnO₂) have an effect onreducing the ferric iron (Fe+++) to the ferrous iron (Fe++) to increasethe redox ratio. More particularly and with reference to FIGS. 4-7 asneeded there is shown connected data points providing graph curves forsoda-lime-silica low iron containing glass. The graph curves 130, 132,134, and 136 of FIG. 4 show connected data points for samples havingvarying amounts of tin dioxide in the range of 0 to 0.2 wt. %, andgraphite in the amounts of 0 wt. % (curve 136), 0.025 wt. % (curve 134),0.050 wt. % (curve 132) and 0.075 wt. % (curve 130). The glass sampleswere heated to a temperature of 2650° F. Graph curve 136 shows theincrease of the redox ratio by increasing the tin dioxide and having 0wt % graphite. The data points for the graph curves 130, 132, 134, and136 at 0 wt % tin dioxide show an increase in the redox ratio forincreases of graphite. The graph curves 130, 132, 134, and 136 show anincrease in the redox ratio for increases in graphite and tin dioxidethat out perform increases of graphite and tin dioxide alone.

FIG. 5 shows three graph curves 136, 138 and 140 for samples that didnot contain graphite additions to highlight the effects of temperature.The graph curve 136 is also shown in FIG. 4 and shows an increase in theredox ratio by increasing the tin dioxide. In FIG. 5 the graph curve 136shows an increase in the redox ratio as the tin dioxide is increased andthe redox ratio for glass melted at 2650° F. Graph curve 138 shows anincrease in the redox ratio as the tin dioxide increases with a meltingtemperature of 2800° F., The graph curves 136 and 138 show an increasein the redox ratio for a higher melting temperature, and tin dioxidethat out perform the lower melting temperature and tin dioxide. Thegraph curve 140 shows data points for melted glass cullet having tindioxide alone. Graph curve 140 shows that tin dioxide can be added tothe glass batch by additions of glass containing tin oxide, e.g. glasshaving a coating of tin oxide and/or tin dioxide within the body of theglass.

The graph curves of FIG. 6 include the graph curves 132, 142, 144 and146 to show the performance of tin dioxide (curve 146), tin oxide (curve142) and tin metal (curve 144) compared to graph curve 132 discussedabove. From the data points shown in FIG. 6 the tin metal provides thehighest redox ratio. In one non-limiting embodiment of the inventionSnO₂ in the glass composition is in the range of greater than 0 to 0.70wt. %, and preferably greater than zero to 0.60 wt. % or greater than0.015 to 0.58 wt. %. The SnO₂ in addition to increasing the redox ratiois expected to act as a fining agent and reduce the seeds in the glass.

FIG. 7 shows a comparative set of measurements between low iron glasses(graph curve 148) produced during a plant trial in a real furnace underreal operating conditions to low iron glasses from laboratory melts(graph curves 132, 136-138 and 140). The results from the plant trialindicate the laboratory samples can be used to describe the effects ofSnO₂ concentration on iron redox under real processing conditions. Theredox is higher for the plant trial due to higher furnace temperaturesnear 2950° F. vs. the highest temperature of 2800° F. in the laboratory.The plant trial samples were made under the following operatingconditions: 490 tons of glass per day, SnO₂ was added as dry powder to aslurry and mixed into the batch materials, ˜15% cullet that did not haveSnO₂, melting temperature near 2950° F., water content in the glass near500 ppm, floated and formed on a tin bath, glass was annealed.

With reference to FIG. 8 there is shown a set of graph curves 150-164showing changes in the redox ratio for changes in tin dioxide for highiron glasses with Fe₂O₃ content near 0.52wt. %. The graph curves 150-154provide data on redox effects from tin dioxide content, temperaturechanges and changes in wt % of graphite. More particular, the graphcurve 150 shows redox changes with tin additions, the glass melted at2650° F. and no graphite; the graph curve 151 shows redox changes withtin additions, the glass melted at 2800° F. and has no graphite; thegraph curve 152 shows redox changes with tin additions, the glass meltedat 2650° F. and 0.06 wt. % graphite; the graph curve 153 shows redoxchanges with tin additions, the glass melted at 2650° F. and 0.10 wt. %graphite, and the graph curve 154 shows redox changes with tinadditions, the glass melted at 2850° F. and 0.15 wt. % graphite. Thedata point 152A provides a base line for 0 wt. % tin dioxide.

From the information provided by FIGS. 4-8, it can now be appreciatedthat the invention is not limited by the amount of tin and/or tincontaining compound added to oxidize the ferrous iron (Fe++) to ferriciron (Fe+++) to reduce the redox ratio of the glass being made. Moreparticularly Sn and tin containing compounds can be used alone, incombination with carbon, e.g. but not limited graphite, coal and/or oil,altering the glass batch melting temperature and combinations thereof.In the practice of non-limiting embodiments of the invention, the tinand tin containing compounds provide tin in the range of greater thanzero to 5 wt. %; 0.10 to 4 wt. %, 0.4 to 3 wt. % and any wt. % withinthe rages recited.

Shown in Tables 3-7 is a range of glass compositions and approximatebatch component ranges with SnO₂ and/or graphite to make the low iron,high redox ratio glass of the invention.

Table 3 is a range of glass compositions including SnO₂ and graphite,and corresponding batch ingredients to make the glass.

TABLE 3 Min Max Minimum Maximum Ingredient (lbs) (lbs) Ingredient Wt. %Wt. % sand 1000 1000 SiO₂ 65.00 80.00 soda ash 200 400 Na₂O 10.00 20.00limestone 40 100 CaO 5.00 15.00 dolomite 100 400 MgO 0.00 8.00 salt cake0 20 SO₃ 0.00 1.000 SnO₂ 0.07 40 Fe₂O₃ 0.00 0.0200 graphite 0 8 Al₂O₃0.00 5.00 K₂0 0.00 5.00 SnO₂ 0.0050 2.00

Table 4 is a glass composition and approximate batch ingredient weightswithout SnO₂ and with graphite.

TABLE 4 Ingredients lbs. Ingredient Wt. Wt. % sand 1000.00 SiO₂ 997.5073.30 soda ash 316.00 Na₂O 188.06 13.82 limestone 88.00 CaO 120.42 8.85dolomite 234.00 MgO 51.45 3.78 salt cake 9.50 SO₃ 2.67 0.197 graphite1.00 Fe₂O₃ 0.10 0.0077 Al₂O₃ 0.50 0.04

Table 5 is a preferred glass composition and approximate batchingredient weights with SnO₂ and graphite.

TABLE 5 Ingredients lbs. Ingredient Wt. Wt. % sand 1000.00 SiO₂ 997.5073.18 soda ash 320.00 Na₂O 190.39 13.97 limestone 80.00 CaO 117.76 8.64dolomite 240.00 MgO 52.72 3.87 salt cake 9.50 SO₃ 2.67 0.196 SnO₂ 0.70Fe₂O₃ 0.31 0.0230 Graphite 0.70 Al2O₃ 0.50 0.04 SnO₂ 0.6913 0.0507

Table 6 shows a preferred range of colorants and/or redox controllingagents:

TABLE 6 Ingredients Amount Nd₂O₃ 0-0.1 wt. % CoO 0-40 ppm Fe₂O₃ 0-0.02wt. % Cr₂O₃ 0-0.05 wt. % TiO₂ 0-0.05 wt. % CeO₂ 0-1 wt. % MnO₂ 0-1 wt. %

The invention contemplates the lower range of all or selected ones ofthe ingredients of Table 6 to have a lower range of greater than 0.

Shown in Table 7 is an example of a glass composition of the inventionwith 0.075 wt. % graphite in the batch and 0.1 wt. % tin dioxide addedto the batch with a melting temperature of 2650° F. and the performance:

TABLE 7 Ingredient Ingredient in wt. % SiO₂ 73.11 Na₂O 13.65 K₂O 0.01CaO 8.68 MgO 3.16 Al₂O₃ 0.03 Fe₂O₃ 0.0097 SrO 0.02 SO₃ 0.2 ZrO₂ 0.001FeO/Fe₂O₃ 0.505 SnO₂ 0.111

The glass sample in Table 7 had an LTA of at least 91.23%; a dominantwavelength in the range of 490-500, e.g. 496.66 nanometers; anexcitation purity in the range of 0.10 to 0.15, e.g. 0.14%; a TSUV inthe range of 85-93%, e.g. 89.07%; a TSIR in the range of 85-90%, e.g.87.82% and a TSET in the range of 87-91%, e.g. 89.43% at a thickness of5.6 mm. Similar compositions would be expected to exhibit LTA greaterthan or equal to 85%, DW in the range of 480 nm to 510 nm at 5.5 mmequivalent thickness for glass from 2 mm to 25 mm sheet thickness. Theradiation transmittance data would be based on TSUV 300-390 nanometers;LTc 400-770 nanometers and TSIR 800-2100 nanometers.

In another non-limiting embodiment of the present invention, the presentinvention is practiced to make a high iron Fe₂O₃, high redox glass, e.g.but not limited to the type disclosed in U.S. Pat. No. 6,313,053 thatprovides a blue colored glass using a standard soda-lime-silica glassbase composition and additionally iron and cobalt, and optionallychromium, as solar radiation absorbing materials and colorants. Inparticular, the blue colored glass includes about 0.40 to 1.0 wt. %total iron as Fe₂O₃, preferably about 0.50 to 0.75 wt %, about 4 to 40PPM CoO, preferably about 4 to 20 PPM, and 0 to 100 PPM chromium oxide(“Cr₂O₃”). The redox ratio for the glass of the present invention isgreater than 0.2 to 0.60, and preferably between 0.35 to 0.50. In oneparticular embodiment of the invention, the glass has a luminoustransmittance of at least 55% and a color characterized by a dominantwavelength of 485 to 489 nanometers and an excitation purity of about 3to 18 percent. In another embodiment of the invention, the glass has aluminous transmittance of at least 65% at a thickness of about 0.154inches (3.9 mm) and a color characterized by a dominant wavelength of485 to 492 nanometers and an excitation purity of about 3 to 18 percent.

Shown in Tables 8-12 are a range of glass compositions and approximatebatch component ranges with SnO₂ and graphite compositions andapproximate batch component ranges with SnO₂ and graphite to make thehigh iron, high redox ratio glass of the invention.

Table 8 is a range of glass compositions including SnO₂ and excludinggraphite, and corresponding batch ingredients to make the glass.

TABLE 8 Min Max Minimum Maximum Ingredient (lbs) (lbs) wt. % wt. % sand1000 1000 SiO₂ 65.00 80.00 soda ash 200 400 Na₂O 10.00 20.00 limestone40 100 CaO 5.00 15.00 dolomite 100 400 MgO 0.00 8.00 salt cake 0 20 SO₃0.10 1.00 SnO₂ 0.07 77 Fe₂O₃ 0.10 2.0 graphite 0 8 Al₂O₃ 0.00 5.00 rouge0 33 K₂0 0.00 5.00 SnO₂ 0.0050 5.0

Table 9 is a glass composition and approximate batch ingredient weightswithout SnO₂ and with graphite.

TABLE 9 Ingredient lbs. wt. wt % sand 1000.00 SiO₂ 997.50 72.83 soda ash316.00 Na₂O 188.06 13.73 limestone 88.00 CaO 120.42 8.79 dolomite 234.00MgO 51.45 3.76 salt cake 9.50 SO₃ 2.67 0.195 graphite 2 Fe₂O₃ 6.87 0.502rouge 6.8 Al₂O₃ 2.00 0.15

Table 10 is a preferred glass composition and approximate batchingredient weights with graphite and SnO₂.

TABLE 10 Ingredient wt. wt. % sand 1000.00 SiO₂ 997.55 71.89 soda ash320.00 Na₂O 190.39 13.72 limestone 80.00 CaO 117.76 8.49 dolomite 240.00MgO 52.72 3.80 salt cake 9.50 SO₃ 2.67 0.193 SnO₂ 17.42 Fe₂O₃ 6.49 0.468Graphite 1 Al₂O₃ 2.00 0.14 rouge 6.4 SnO₂ 17.20 1.23

Table 11 shows preferred ranges of colorants and/or redox controllingagents.

TABLE 11 Ingredients Amount Nd₂O₃ 0-0.5 wt % CoO 0-80 ppm Fe₂O₃ 0.01-2.0wt % Cr₂O₃ 0-1 wt % TiO₂ 0-1 wt % CeO₂ 0-1 wt % MnO₂ 0-1 wt %

The invention contemplates the lower range of all or selected ones ofthe ingredients of Table 11 to have a lower range of greater than 0.

Shown in Table 12 is an example of a glass composition of the inventionand the expected performance.

TABLE 12 Ingredients Ingredients in wt. % SiO₂ 71.83 Na₂O 13.94 K₂O 0.07CaO 8.73 MgO 3.8 Al₂O₃ 0.07 Fe₂O₃ 0.515 SrO 0.003 SO₃ 0.18 ZrO₂ 0.0012FeO/Fe₂O₃ 0.559 SnO₂ 0.828

The glass sample in Table 12 had an LTA of at least 65.19%; a dominantwavelength in the range of 485-490 nanometers, e.g. 487.95 nanometers;an excitation purity in the range of 10-15%, e.g. 13.13%; a TSUV in therange 45-50%, e.g. 48.46%; a TSIR in the range of 7-9%, e.g. 8.25% and aTSE T in the range of 32-36%, e.g. 34.59% at a thickness of 5.6 mm.Similar samples are expected to have a redox of greater than 0.35 up toabout 0.60, a luminous transmittance of at least 55 percent, and a colorcharacterized by a dominant wavelength of 485 to 489 nanometers and anexcitation purity of about 3 to 18 percent, and wherein the glass has atotal solar ultraviolet transmittance of about 60 percent or less, atotal solar infrared transmittance of about 35 percent or less and atotal solar energy transmittance of about 55 percent or less at athickness of about 0.154 inches.

As can be appreciated, the invention is not limited to the non-limitedembodiments of the invention disclosed herein and the invention can bepracticed on glasses having medium wt. % of total iron, e.g. greaterthan 0.02 to less than 0.10 wt. %, and having redox ratio less than 0.2to 0.6.

With reference to FIG. 9, as can be appreciated by those skilled in theart, the glass of the invention made using the float process, whichincludes supporting and advancing a glass ribbon 170 on a molten tinbath 172 while controllably cooling and applying forces to the glassribbon 170 has an air side 174 and an opposite tin side 176. The tinside 176 is the side of the glass ribbon 170 supported on the molten tinbath 172. The tin dioxide concentration generally is higher at the tinside 176 (tin dioxide concentration at the tin side 172 designated bythe number 178) of the glass ribbon 170 than the tin dioxideconcentration in body portion 180 of the glass ribbon 170. A reason forthe difference in tin concentration is that the tin dioxideconcentration 178 at the tin side 176 of the glass ribbon 170 includesthe tin added to the batch and/or molten glass to maintain a high redoxratio for the glass ribbon 170 and the tin from the tin bath 172 thatdiffuses into the tin side 176 of the glass ribbon 170 as discussedabove; whereas, the tin concentration in the body portion 180 of theglass ribbon is the tin dioxide added to the batch and/or molten glassto maintain a high redox ratio for the glass ribbon 170. As can beappreciated the transition between the tin dioxide concentration at thetin side 176 and the tin concentration in the body portion 180 is shownin FIG. 9 as a straight line 182 for purposes of clarity; however, thetransition 182 is not a straight line but a gradual transition havingdecreasing concentration of tin as the distance from the surface 184 ofthe tin side increases. Further as the thickness of the glass ribbonincreases, the thickness of the tin dioxide concentration at the tinside of the glass ribbon can increase. As can now be appreciated, theaddition of tin and/or tin containing compounds may result in tin beingextracted from the tin side of the ribbon resulting in the concentrationof the tin ions at the tin side of the ribbon being equal to or lessthan the tin ions in the air side of the glass ribbon.

It will be readily appreciated by those skilled in the art thatmodifications can be made to the invention without departing from theconcepts disclosed in the foregoing description. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention, which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

What is claimed is:
 1. A method of making a glass, comprising: providinga basic soda-lime-silica glass portion, and a colorant portion, thecolorant portion, comprising: total iron as Fe₂O₃ in the range ofgreater than zero to 2.00 weight percent, a redox ratio in the range of0.20 to 0.60, and tin and/or tin containing compounds providing tin inan amount within the range of greater than 0.005 to 5.0 weight percent;melting the glass portion and the colorant portion to provide a pool ofmolten glass; flowing the molten glass onto a molten tin bath; movingthe molten glass on the surface of the molten tin bath, whilecontrollably cooling the glass and applying forces to the glass toprovide a glass of a desired thickness, and removing the glass from themolten tin bath, wherein the tin and/or tin containing compoundsconcentration at the tin side of the glass are greater than the Snconcentration in body portion of the glass, the body portion of theglass extending from the air side of the glass and terminating short ofthe tin side of the glass.
 2. The method according to claim 1 whereinthe total iron as Fe₂O₃ is selected from the group of total iron asFe₂O₃ in the range of greater than zero to 0.02 weight percent.
 3. Themethod according to claim 2 wherein the glass has a redox ratio in therange of 0.36 to 0.60 and comprises: Min Max Minimum Maximum Ingredient(lbs.) (lbs.) Ingredient Wt. % Wt. % sand 1000 1000 SiO₂ 65.00 80.00soda ash 200 400 Na₂O 10.00 20.00 limestone 40 100 CaO 5.00 15.00dolomite 100 400 MgO 0.00 8.00 salt cake 0 20 SO₃ 0.00 1.000 SnO₂ 0.0740 Al₂O₃ 0.00 5.00 graphite 0 8 K₂0 0.00 5.00 SnO₂ 0.0050 2.00


4. The method according to claim 3 wherein the colorant portioncomprises CoO 0-5 parts per million; Nd₂O₃ in the range of 0-0.1 weightpercent: and CuO 0-0.03 weight percent, wherein the colorant portionprovides the glass with a total solar energy transmission (“TSET”) ofgreater than 0% and equal to or less than 5%, a total solar energyreflection (“TSER”) of greater than 3% and equal to or less than 7%, anda total solar energy absorption (“TSEA”) of greater than 90% and equalto or less than 97%, and selected ones of the TSET, TSER, and TSEA aremeasured over a wavelength range of 300 to 2500 nanometers (“nm”) at aglass thickness in the range of 3.6-4.1 millimeters (“mm”).
 5. Themethod according to claim 4 wherein tin and tin containing compounds areadded to the glass batch materials and/or molten glass by an actselected from (1) adding SnO₂ and/or tin sulfate (“SnS”) to the glassbatch materials as a dry powder; (2) adding pellets of SnO₂ to the glassbatch materials; (3) adding glass cullet to the batch material, thecullet having a coating of SnO₂ over and/or on a glass surface and/orglass cullet having tin and/or tin containing compounds within the bodyof the glass; (4) adding ground particles of tin and/or tin containingcompounds, e.g. but not limited to Sn, SnO₂, and SnS to the glass batchmaterials; (6) mixing dry SnO₂ with a liquid to make a slurry and addingthe slurry to the batch materials; (7) bubbling tin containing halogengas into the molten glass, and (8) adding organo-tin compounds andorgano-tin compounds containing halogens.
 6. The method according toclaim 1 wherein the total iron as Fe₂O₃ is in the range of greater than0.02 weight percent to 0.10 weight percent.
 7. The method according toclaim 6 wherein the glass wherein the glass has a redox ratio in therange of 0.36 to 0.60 and comprises: SiO₂ 65-75 wt. % Na₂O 10-20 wt. %CaO 5-15 wt. % MgO 0-5 wt. % Al₂O₃ 0-5 wt. % K₂O 0-5 wt. %; and

total iron as Fe₂O₃ selected from total iron as Fe₂O₃ in the range ofgreater than 0.02 weight percent to less than 0.10 weight percent, andthe tin and/or tin compound at the air side has a concentration of tinin the range of 0.1-3 wt. %.
 8. The method according to claim 1 whereinthe total iron as Fe₂O₃ is in the range of 0.10 to 2.00 weight percent.9. The method according to claim 8 wherein the glass wherein the glasshas a redox ratio in the range of 0.36 to 0.60 comprises Min Max MinimumMaximum Ingredient (lbs.) (lbs.) wt. % wt. % sand 1000 1000 SiO₂ 65.0080.00 soda ash 200 400 Na₂O 10.00 20.00 limestone 40 100 CaO 5.00 15.00dolomite 100 400 MgO 0.00 8.00 salt cake 0 20 SO₃ 0.10 1.00 SnO₂ 0.07 77Fe₂O₃ 0.10 2.0 graphite 0 8 Al₂O₃ 0.00 5.00 rouge 0 33 K₂0 0.00 5.00SnO₂ 0.0050 5.0


10. The method according to claim 1 wherein tin and tin containingcompounds are added to the glass batch materials and/or molten glass byan act selected from selected from (1) adding SnO₂ and/or tin sulfate(“SnS”) to the glass batch materials as a dry powder; (2) adding pelletsof SnO₂ to the glass batch materials; (3) adding glass cullet to thebatch material, the cullet having a coating of SnO₂ over and/or on aglass surface and/or glass cullet having tin and/or fin containingcompounds within the body of the glass; (4) adding ground particles oftin and/or tin containing compounds, e.g. but not limited to Sn, SnO₂,and SnS to the glass batch materials; (6) mixing dry SnO₂ with a liquidto make a slurry and adding the slurry to the batch materials: (7)bubbling tin containing halogen gas into the molten glass, and (8)adding organo-tin compounds and organo-tin compounds containinghalogens.
 11. The method according to claim 10 wherein the glass has aredox of greater than 0.35 up to about 0.60, a luminous transmittance ofat least 55 percent, and a color characterized by a dominant wavelengthof 485 to 489 nanometers and an excitation purity of about 3 to 18percent, and wherein the glass has a total solar ultraviolettransmittance of about 60 percent or less, a total solar infraredtransmittance of about 35 percent or less and a total solar energytransmittance of about 55 percent or less at a thickness of about 0.154inches.
 12. The method according to claim 1 wherein the glass has waterin the range of 200 to 700 parts per million.
 13. The method accordingto claim 1 wherein the glass has an LTc of 90.8%; a dominant wavelengthof 490.50 nanometers; an excitation purity of 0.27%; a TSUV of 88.4%; aTSIR of 86.4% and a TSET od 88.5% and the radiation transmittance datais based on TSUV 300-390 nanometers; LTc 400-770 nanometers and TSIR800-2100 nanometers at a standard thickness of 5.5 mm.
 14. The methodaccording to claim 1 wherein the glass comprises: IngredientsIngredients in wt. % SiO₂ 71.83 Na₂O 13.94 K₂O 0.07 CaO 8.73 MgO 3.8Al₂O₃ 0.07 Fe₂O₃ 0.515 SrO 0.003 SO3 0.18 ZrO2 0.0012 FeO/Fe₂O₃ 0.559SnO₂ 0.828

wherein the glass has an LTA of at 65.19%; a dominant wavelength of487.95 nanometers; an excitation purity of 13.13%; a TSUV of 48.46%; aTSIR of 8.25% and a TSET of 34.59% at a thickness of 5.6 mm.